Depends on a lot of things like is he married? How much does his wife make? Does he have children? How many children? There are a lot of variables but generally the more money you make, the higher tax bracket you creep up into.
This issue has been widely discussed in our area with many comparing paychecks and the general consensus is that from about 5 to 7 hours you receive the most from your overtime worked. After that the percentage of money coming to you falls way off and the amount to taxes greatly increases. Several co-workers after a contract pay increase actually saw their takehome decrease for the same amount of OT worked as in the past. We figured based on their withholdings and marital status they got kicked into a higher bracket but the odd thing was when 1 of them increased their 401k deduction they then saw the OT takehome go up above what it was prior to the raise. Can't explain how they break all that stuff down but for those with 401k's it is worth considering.
Start looking at your checks or if you don't keep you check stubs go to UPSers.com and you can view the last 6 months of your checks and compare the amounts based on overtime worked and unless you have some special circumstance you will probably find the same thing we did.
Several co-workers said instead of all these brainstorm ideas of new ways to tax or not to tax they should just make OT tax free. Although I agree the sound of that sure is nice I doubt it will ever happen.